Nokia has announced that starting with version 4.5, Qt will be available under the LGPL 2.1. From the announcement,

The move to LGPL licensing will provide open source and commercial developers with more permissive licensing than GPL and so increase flexibility for developers. In addition, Qt source code repositories will be made publicly available and will encourage contributions from desktop and embedded developer communities. With these changes, developers will be able to actively drive the evolution of the Qt framework.

This exciting change, made with consultation of the
KDE Free Qt Foundation, should encourage KDE and Qt use among commercial and proprietary developers and makes the philosophy of "Qt Everywhere" complete.

Kai Öistämö, Executive Vice President of Devices at Nokia expands,

"By opening Qt’s licensing model and encouraging more contributions, Qt users will have more of a stake in the development of Qt, which will in turn encourage wider adoption."

The change in licensing for Qt is happening under the mantra "Qt
Everywhere" and is a step to remove any and all possible blocking objections
for not using Qt. Nokia explains further,

Qt will be available under the LGPL version 2.1 with the upcoming Qt 4.5 release. Qt will also continue to be licensed under commercial license terms, as well as the GPL, version 3.0.

Nokia will also be opening up the development of Qt. A clear path for the
extension of external contributions is currently being built, including
publicly available source code repositories and access to the same level of
support, independent of the license.

The simple fact behind this is that Nokia is less reliant on the
income from Qt licensing than Trolltech (now Qt Software) was, and this has
given Qt Software more room to approach the market with more permissive
licensing strategies in order to increase adoption of the Qt toolkit.
This is part of the 10x growth target announced at last year's Akademy
to achieve ten times as many developers and ten times as many free software community users.
Or as KDE and Qt developer Thiago Maciera put it "we want KDE to be ten times as big".

While kdelibs has always been available under the LGPL, this marks the first
time that both Qt and kdelibs will both be available under the LGPL.
This will help make the licensing of KDE's libraries more permissive, flexible
and coherent. KDE's licensing is summarised on
href="http://techbase.kde.org/index.php?title=Policies/Licensing_Policy">TechBase,
and can be described as "LGPL or equivalent for libraries, GPL otherwise".

Meanwhile, Nokia reiterates their commitment to a commercially viable and,
technology-wise, best-of-breed toolkit. In fact, the performance and
functionality improvements that can be seen in the upcoming Qt 4.5 release are
impressive. Running KDE 4.2 with Qt 4.5 is already being tested by several
engineers inside Qt software, which has resulted in a number of bug fixes in
both KDE and Qt. Independent of the licensing changes, the KDE release team
plans to update the version of Qt in KDE's development tree (qt-copy) shortly
to snapshots of Qt 4.5 which is due to be released in March.

All-in-all today's news means tremendous things for Free and Open Source software. The
possibility of extending the reach of all of our work is exciting in and of
itself, and this announcement could lead to a veritable explosion of Qt and
KDE adoption.

The ideal way to merge KDE and GNOME is to build Qt on top of Glib such that there is absolutely no redundancy between the two (ie. ASCII conversion, File access, etc). This way Qt apps won't incur a memory penalty if Qt is compiled with Glib support.

QtCore should rely on Glib to do the low-level stuff. Unfortunately this will mean sacrifices on all sides (ie. GTK will need to die), but eventually will lead to a unified Free Desktop.

I think it is impossible to have one toolkit like it is impossible to have only one distro, but since both toolkits will be licenced under LGPL now, i would like to see them share features/ideas, talk to each other and have some standarts. As a user, i want GTK+ and Qt applications to have the same functionality under Gnome and KDE (for example: look and feel, file open dialogs, ability to use drag and drop, which sometimes does not work). It would be great. But it seems that (sadly) toolkit developers have no interest in that (Qt will have a GTK style in 4.5, but there is no response from GTK+ developers) and don't see anything happening soon.

I think most people misunderstand the press info. Adding LGPL as a license option allow developers to use Qt for commercial purposes without having to pay a license for Qt. Now you only pay for the support. That will bring more developers to the platform, and probably more programs for Linux, and that's good news.

What means for Gnome: probably nothing. While they are talking about breaking ABI compatibility with 3.0, is not the same as switching a toolkit. To clear a concept to non programmers:
A. Breaking API/ABI compatibility means that they are free to add new library calls and change old ones (arguments, return values, etc) so that an older application will likely not work unless a programmer fix the calls.
B. Rewriting means throwing everything to the basket and start from scratch. And thats not what Gnome/Gtk developers have been talking about.

In short, if they are not rewriting Gtk, less they are going to switch the framework.